Method and apparatus for the power control system outer loop of a mobile communications system

Abstract

Method and apparatus for the power control system outer loop of a mobile communications systems in a cellular infrastructure that allows fulfilling a given Quality of Service (QoS) with the minimum power level necessary. This outer loop is in charge of setting the desired signal to interference target ratio SIR tgt that fulfils the required quality of service in a radioelectric environment characterised by stochastic models. The proposed method is based on the application of the Newton-Raphson iteration method on numerical approximations of the various outage probability (QoS) probability density functions in various propagation environments, so that having established this probability and dynamically estimated the second order moments characteristic of each statistic considered, the margin over the SIR median is obtained and thereby the SIR tgt corresponding to the aforementioned outage probability.

1. A method of determining a signal to interference target ratio for operation of the outer loop of a power control system of a mobile communications system with a cellular infrastructure, wherein the ratio is determined based on a signal received from one of a base station and a mobile station of the mobile communications system, the method comprising:
 estimating the desired signal to interference ratio of the received signal; 
 estimating the following statistical moments of the desired signal to interference ratio: typical deviation of the slow or lognormal fading component, typical deviation of the Gaussian distribution describing the joint statistical variation of all interfering signals, and, in the case of a direct beam existing between the emitter and the receiver, the Rice factor, comprising the quotient of the deterministic component and the random component of the desired signal; 
 based on the estimated statistical moments and on a specification of the outage probability, calculating the margin of the desired signal to interference ratio by the Newton-Raphson iteration method; and 
 determining the desired signal to interference target ratio for the outer loop based on the calculated margin. 
 
   
   
     2. The method according to  claim 1 , further comprising using the numerical approximation for the probability distribution function corresponding to the desired signal to interference ratio of a communication without a direct beam between the emitter and the receiver, wherein the Newton-Raphson method is applied to obtain the margin of the ratio that will fulfil an outage probability specification, for statistical conditions determined by the typical deviation of the slow or lognormal fading component and the typical deviation of the Gaussian distribution that describes the joint statistical variation of all the interfering signals. 
   
   
     3. The method according to  claim 2 , further comprising numerically integrating the probability density function corresponding to the desired signal to interference ratio of a communication without a direct beam between the emitter and the receiver, thereby obtaining an expression for the outage probability with the statistical conditions typical deviation of the slow or lognormal fading component and the typical deviation of the Gaussian distribution that describes the joint statistical variation of all the interfering signals, wherein the expression is suitable for a subsequent application of the Newton-Raphson method. 
   
   
     4. The method according to  claim 2 , further comprising numerically integrating the probability density function corresponding to the desired signal to interference ratio of a communication with a non-zero deterministic component corresponding to the existence of a direct beam between the emitter and the receiver, thereby obtaining an expression for the outage probability with the statistical conditions including typical deviation of the slow or lognormal fading component, typical deviation of the Gaussian distribution that describes the joint statistical variation of all the interfering signals, and the Rice factor, so that the expression is suitable for a subsequent application of the Newton-Raphson method. 
   
   
     5. The method according to  claim 1 , further comprising using the numerical approximation for the probability distribution function corresponding to the desired signal to interference ratio of a communication with a non-zero deterministic component corresponding to the existence of a direct beam between the emitter and the receiver, wherein the Newton-Raphson method is applied to obtain the margin of the ratio that will fulfil an outage probability specification for statistical conditions determined by the typical deviation of the slow or lognormal fading component and the typical deviation of the Gaussian distribution that describes the joint statistical variation of all the interfering signals and the Rice factor. 
   
   
     6. An apparatus for implementing the outer loop of the power control system of a mobile communications system with a cellular infrastructure, comprising:
 a receiver configured to receives a signal from one of a base station and a mobile station of the mobile communications system; 
 a processor configured to implement an operational method for the outer loop of the power control system, 
 wherein the processor is configured to estimates the following statistical moments of the desired signal to interference ratio: typical deviation of the slow or lognormal fading component, typical deviation of the Gaussian distribution that describes the joint statistical variation of all the interfering signals, and the Rice factor, comprising the quotient of the deterministic component and the random component of the desired signal; 
 wherein the processor is further configured to calculate, based on these statistical moments and an outage probability specification, a margin of the desired signal to interference ratio by the Newton-Raphson iteration method; and 
 wherein the processor is further configured to determine, based at least in part on the calculated margin, the desired signal to interference target ratio for the aforementioned outer loop. 
 
   
   
     7. The apparatus according to  claim 6 , further comprising an emitter configured to send the power control information to the base station if the apparatus is in the mobile station, or to the mobile station if the apparatus is in the base station. 
   
   
     8. The apparatus according to  claim 6 , wherein the processor calculates the desired signal to interference ratio by the Newton-Raphson iteration method, and wherein the desired signal to interference ratio fulfils a given outage probability specification for statistical conditions characterised by the estimated statistical moments. 
   
   
     9. A computer readable medium having a program for executing a method of determining a signal to interference target ratio for operation of the outer loop of a power control system of a mobile communications system with a cellular infrastructure, wherein the ratio is determined based on a signal received from one of a base station and a mobile station of the mobile communications system, the method comprising:
 estimating the desired signal to interference ratio of the received signal; 
 estimating the following statistical moments of the desired signal to interference ratio: typical deviation of the slow or lognormal fading component, typical deviation of the Gaussian distribution describing the joint statistical variation of all interfering signals, and, in the case of a direct beam existing between the emitter and the receiver, the Rice factor, comprising the quotient of the deterministic component and the random component of the desired signal; 
 based on the estimated statistical moments and on a specification of the outage probability, calculating the margin of the desired signal to interference ratio by the Newton-Raphson iteration method; and 
 determining the desired signal to interference target ratio for the outer loop based on the calculated margin.